This invention pertains to the art of coreless induction furnaces such as those that contain a replaceable refractory hearth lining, and more particularly to a method and system for extracting the lining from the furnace.
The invention is particularly applicable to an induction melting furnace in which a furnace content to be heated is supported in a refractory hearth. Sometimes the lining material itself or the furnace content may be dangerous or harmful so that when it is necessary to replace the refractory lining, the lining should be contained for transport and ultimate disposal. The invention is particularly applicable to a method and system for extracting such a lining from the furnace and placement in a container for transport, storage or ultimate disposal. However, it will be appreciated by those skilled in the art that the invention could be readily adapted for use in other environments as, for example, where cumbersome and potentially harmful linings are to be replaced and contained upon extraction from a furnace or other device.
Refractory linings that are employed as hearths useful for such induction melting furnaces are typically composed of fire-proof materials commonly referred to as dry ram type refractories such as silica, alumina or magnesia. The linings have to be replaced at regular intervals so the safety, convenience and efficiency of the replacement process are important considerations. In particular, where the furnace work content is a dangerous and harmful item, such as one that has been radioactively contaminated, minimal safety precautions require containment of the refractory lining during both extraction of the lining from the furnace and subsequent transport, storage and disposal.
Prior known systems for refractory extraction and discharge have met with varying degrees of success. Such systems and methods have included lifting the refractory lining by means of a crane from the furnace cavity, dismantling of the furnace floor so that the lining can be pushed out or breaking up of the refractory lining with pneumatic hammers. U.S. Pat. No. 4,334,857 discloses a method and system where a push-out device, acting underneath the furnace floor, pushes out the furnace lining upon cooling of the lining so that a separation occurs between the furnace sidewalls and the lining.
None of the foregoing prior art systems are useful with regard to the controlled extraction and containment of a dangerous lining material or a lining which has been contaminated by a harmful furnace content. All the methods will involve uncontained extraction and/or breaking up of the crucible. Also, the ejection device of the '857 patent involves a substantial modification of a furnace floor which is undesirable from the standpoint of furnace construction.
The present invention contemplates a new and improved refractory extraction system and method which overcomes the above problems and provides improved safety and economy of construction and yet is simple in design so that refractory replacement can be easily accomplished while safe containment of a contaminated lining is maintained.